A measuring resistor, also called shunt resistor, is used to measure an electric current. The measuring resistor is inserted into the current path for this purpose. In order to have the lowest possible ohmic losses, this resistor generally has a very small value, for example in the milliohms (mΩ) range.
High currents are often to be measured in the field of power components. In the context of this application, high current is understood to mean an electric current of from approximately one ampere to hundreds of amperes.
A current measurement can be used for example to control a component, i.e. the current measurement is used in a feedback loop. Furthermore, there are many further applications in which a high current is to be measured, for example in the laboratory during development/qualification. A purely ohmic resistance is desirable for a current measurement, i.e. an ohmic resistance having no parasitic components such as, in particular, parasitic inductances. Parasitic elements in a power loop, i.e. for example in a high-current path, can lead to overvoltage spikes and bring about an increased stress on components. Said stress can, for example if a voltage breakdown occurs, damage semiconductors.
One exemplary field of application for a measuring resistor for a high-current measurement is voltage converters. Parasitic elements, in particular inductances, reduce the efficiency of the converters. The inductances can form resonant circuits which lead to superposed oscillations. Oscillations reduce the signal-to-noise ratio of the measurement. That is to say that it becomes necessary to filter the measurement signal. A low-pass filter is required for this purpose. This filtering reduces the dynamic range of the control loop, or in other words the response time is artificially increased.
The lengthening of the response time that is necessary owing to the parasitic elements has the effect that time-critical functions, such as, for example, protective functions in the form of turn-off in the event of overcurrent, have to have an artificially low response threshold in order to compensate for the longer loop time. Thus, the performance of a power switch cannot be fully utilized.
For these and other reasons, there is a need for the present invention.